This invention relates to a switching arrangement for use in a time division multiple access (TDMA) network comprising a plurality of earth stations.
In conventional time division multiple access network of the type described, communication is made among earth stations through a time division multiple access frame which is divisible into a plurality of channels or time slots. More specifically, each of the earth stations can communicate with the other earth stations through a preselected one of the channels that is preassigned to the earth station under consideration and that is determined in accordance with a burst time plan table and a channel assignment pattern table. Both the burst time plan table and the channel assignment pattern table will simply be called a table hereinafter.
It often occurs that such tables should be changed from an old one to a new one when the earth stations or channels are increased or decreased in number. Heretofore, the new table has been distributed in advance from a standard or reference station to all the other earth stations, which will be called terrestrial stations, in some way or another while the earth stations are kept in operation in accordance with the old table. Each of the new table and the old table may be either a combination of the burst time plan table and the channel assignment pattern table or the burst time plan table alone. For this purpose, a table switching signal must be sent from the standard station to be delivered to all of the terrestrial stations. Supplied with the table switching signal, all of the earth stations substantially simultaneously carry out switching operations, switching of the tables from the old one to the new one without any interruption.
When the switching operations of the tables are simultaneously carried out in all of the earth stations, the standard station must confirm or monitor whether or not the switching operations are correctly carried out in all of the terrestrial stations. Such monitoring operation becomes troublesome and time-consuming as the earth stations increase in number.
Recently, it has often been required to locally increase or decrease a channel capacity, as necessary for communication between specific ones of the earth stations. In order to respond to such a requirement, it has been confirmed by the present inventors that the old table need not entirely be changed to a new one but may only need to be locally or partially changed at a portion of the time division multiple access frame related to the local increase or decrease. In other words, the switching operations of the table need not necessarily be carried out in all the earth stations but may only need to be carried out at the specific earth stations influenced by a change of the channel capacity.